I hope you aren't planning to set it up and put fish in it right away. If you are, you need to go to a book store or library and get some beginner's books on aquarium keeping. A newly set up tank must be cycled before adding fish, or they will die. This can take a month or more.
While the tank is cycling you can be looking for, or saving up for, a hood. You could ask the parents to chip in a dollar or two to help with the expense, scour yard sales, ask friends and relatives who might have one in the attic, check out Goodwill and other thrift stores, check the classified ads, or try sites such as Freecycle, Craig's List, or any other local swap site. Even give e-bay a look. There are still good deals to be had there. 10 gallon tanks are so common, it shouldn't take a super sleuth to locate a hood for one. Good luck!
